Electrical devices often comprise cables which extend from one printed circuit board to another or from a printed circuit board to an electrical component. In many instances the cable is a flat flexible cable having a plurality of generally parallel conductors and a flexible insulation disposed around and between the respective conductors. In some instances an electrical connector with terminals therein is mounted to the printed circuit board, such that the terminals of the connector are electrically connected to the conductive areas on the circuit board. A cable may then be terminated to a second electrical connector which can be mated to the board-mounted connector. Connections of this type are employed when it is necessary to periodically separate the cable from the circuit board. However, these mateable pairs of connectors are relatively expensive and can represent a substantial cost penalty in the highly competitive electronics industry. As a result, it is desirable to directly and permanently connect the conductors of the cable to the conductive areas on the circuit board in situations where periodic disconnection will not be required. This direct connection of the cable to the circuit board can result in substantial cost savings and manufacturing efficiencies. In particular, the respective conductive leads of the cable can be soldered directly to the conductive areas on the circuit board without mateable pairs of terminals and connector housings.
The direct connection of the conductive leads in the cable to the conductive areas on the circuit board must provide for strain relief. In particular, stresses exerted on the cable either during assembly of the electrical apparatus or during use of the apparatus may create strains that could damage the soldered connection between the leads of the cable and the conductive areas on the circuit board.
The prior art includes structures to provide strain relief for direct cable to circuit board electrical connections. For example, Japanese Published Patent Application No. 63-31490 shows a molded strain relief structure for mounting directly to a circuit board. The strain relief structure shown in Japanese examined Utility Model Application No. 63-31490 has opposed elongated top and bottom surfaces with an elongated slot extending therebetween for receiving a prepared end of a flat flexible cable. A plurality of angularly aligned fingers extend into the slot for receiving the flat flexible cable. The strain relief structure of Japanese examined Utility Model Application No. 63-31490 is securely mounted to the circuit board in alignment with a linear array of through holes for receiving the conductive leads of the flat flexible cable. The end of the flat flexible is prepared by removing the insulation around and between the conductors adjacent an end of the cable, and the prepared end of the flat flexible cable is inserted into the slot of the board-mounted strain relief structure. Sufficient insertion of the flat flexible cable into the slot of the board-mounted strain relief structure shown in Japanese examined Utility Model Application No. 63-31490 causes the insulation of the flat flexible cable to be urged into engagement with the deflectable locking fingers of the strain relief structure. The exposed leads of the flat flexible cable then can be soldered to appropriate conductive areas on the circuit board.
The structure shown in Japanese examined Utility Model Application No. 63-31490 is undesirable in that it requires the mounting of the strain relief structure onto the circuit board prior to insertion of the flat flexible cable. In particular, the exposed conductors of the flat flexible cable can be damaged or misaligned prior to or during insertion of the flat flexible cable into the strain relief structure shown in Japanese examined Utility Model Application No. 63-31490. Thus, excessive time could be required to ensure alignment of the exposed conductors of the flat flexible cable prior to insertion into the strain relief structure. An improperly aligned exposed lead may not properly enter the through hole of the circuit board, thereby yielding an incomplete circuit. An attempt to realign the conductive leads after a problem has been identified can be extremely difficult both because of the locking engagement of the strain relief structure with the circuit board and because of the strain relief gripping of the insulation inherent in the structure. An attempt to preassemble the flat flexible cable to the strain relief structure of Japanese examined Utility Model Application No. 63-31490 prior to mounting the structure on the circuit board can result in overinsertion of the flat flexible cable and would not avoid the problem of potential damage to the exposed conductive leads which could occur during mounting of the strain relief structure on the circuit board.
Several strain relief structures have included two separate parts that are sandwiched around the ends of the cable to achieve the required strain relief. Examples of these structures are shown in U.S. Pat. No. 4,719,321 which issued to Kozel et al on Jan. 12, 1988 and German printed Patent Application No. 3405 126 which was published on Aug. 14, 1985. Two-part structures such as these are considered undesirable due to generally higher manufacturing costs, complex assembly and inventory control problems. A variation of these two component strain relief structures is shown in U.S. Pat. No. 4,611,868 which issued to Matsui et al on Sept. 16, 1986, and which includes an integrally molded hinged structure which effectively folds around a cable for achieving strain relief.
In view of the above, it is an object of the subject invention to provide a board-mountable strain relief structure.
Another object of the subject invention is to provide an integrally molded board-mountable strain relief structure for cables.
It is an additional object of the subject invention to provide a strain relief structure that can be mounted to a cable for protecting the exposed leads of the cable prior to mounting the cable and the strain relief structure to a circuit board.
A further object of the subject invention is to provide a strain relief structure that can be securely mounted to a cable in a first position during storage and shipment and that subsequently can lockingly engage a cable in a second position to achieve adequate strain relief between the cable and a circuit board.
Still another object of the subject invention is to provide a strain relief structure that prevents overinsertion of the cable in each of two alternate dispositions on the cable.
Another object of the subject invention is to provide a strain relief structure for ensuring protection and alignment of the leads of a cable prior to mounting on a board and that subsequently ensures proper alignment and strain relief connection of the cable to a circuit board.